I've read the whole of the thread and find it very difficult to figure out an appropriate resolution. I don't think there actually is one that would make everyone happy.
Either:
a) Anyone with involuntary tics/noises cannot attend public screenings - obviously unacceptable
or
b) People have no right to expect to be able to concentrate on a movie they have just paid for - not sure this is fair at all either
I think (a) is more unacceptable than (b), but I don't think (b) is particularly compassionate either.
I'm someone who always sits at the back so that I can leave non-disruptively and ask for another viewing if I am finding it impossible to focus on the movie. Have done so on several occasions (loud, chatty teenagers, children running repeatedly up and down aisle throwing popcorn, etc), never disability-related (to my knowledge).
However, I actually wouldn't know if any noise was being made as a result of disability or not, unless I actually asked the person/people involved, and am not entitled to that information anyway (nor do I think it would be appropriate of me to ask).
So, as far as I can rationally work out, either I leave for all distracting levels of noise, or I stay through all of them whether I can watch the movie or not.
Maybe cinemas should sell noise-blocking headphones that can be plugged into the armrest. That way anyone wanting a relatively quieter viewing could have one.